1. Field
Dental instruments equipped with light sources are well-known. Of particular interest herein are dental handpieces and other instruments of a type in which a heat-producing, vibration-sensitive light source is isolated from other portions of the dental instrument.
2. State of the Art
Illumination of a region surrounding the working end of a dental instrument by means of a light source attached directly to the instrument is of significant advantage over the older arrangement of a remotely positioned high-intensity lamp used in combination with a hand-held mirror. In U.S. Pat. No. 3,614,414 to Gores there is described a dental handpiece having a light source within a casing attached to an exterior, rearward end portion of the handpiece. Light is transmitted from the rearward end to the forward or working end of the handpiece by light-guiding means comprising a pair of fiber optic bundles attached along the outside of the handpiece. A disadvantage of a light source and light guide attached to the outside of a dental instrument arises from improper instrument balance so that good tactile control may be difficult to maintain. Also, positioning of the light source along the exterior of the instrument increases the likelihood of contact of a hot portion of the light source casing with the instrument user or with the delicate tissues of a patient's face or mouth.
One attempt at solving the problem of heat generated by a light source mounted on a gas-driven dental handpiece is described in U.S. Pat. No. 3,634,938 to Hutchinson wherein both the compressed air for driving the motor and a stream of water for cooling the operating area are used to cool the light source. This is accomplished by providing a bulky assembly of a cooling coil around the lamp and an air chamber around the lamp and cooling coil through which compressed air passes. The bulky assembly may, however, constitute an impairment to proper tactile control of the instrument by the user. Moreover, cooling a lamp with compressed air may be detrimental to certain types of lamps, especially tungsten-halogen type lamps which must operate at high temperatures for proper efficiency.
A problem especially peculiar to dental handpieces having rotatably driven cutting tools is the vibration generated by the rotating tool and its driving mechanism, such as a high-speed gas-driven motor which typically drives a rotating tool at speeds of 250,000 to 450,000 r.p.m. The vibration transmitted through the handpiece to a bulb mounted on the handpiece may shorten the working life of the lamp filament. Moreover, as a high-speed gas-driven motor attains working speed, there typically occurs a "critical frequency" or a speed of rotation of the motor shaft-and-work tool combination which is at or near the natural frequency of vibration of the lamp filament. Resonant vibration of a lamp filament with the gas-driven motor at the lamp filament critical frequency may quickly destroy a lamp filament. Also, filament-destroying vibrations may be generated during ordinary use of the handpiece when a user forces a rotating bur against a tooth during a cutting or grinding operation, which slows the rotation of the bur and creates "chatter".
There is need, therefore, for a dental instrument having a handle-mounted light source wherein the instrument is thermally isolated from the light source and wherein the light source lamp filament is substantially isolated from vibration generated by a handpiece gas-driven motor or by routine manipulation of the dental instrument.